Solar Energy Lab Description and validation of the Little correlation for boiling zeotropic mixtures in horizontal tubes from cryogenic to room temperature Rodrigo Barrazaa,b, Gregory Nellisa, Sanford Kleina, Douglas Reindla aDepartment of Mechanical Engineering, University of Wisconsin, USA bDepartment of Mechanical Engineering, Universidad Tecnica Federico Santa Maria, Chile

Overview Motivation Little correlation Similar correlations Model derivation Little model final form Validation Applicability criteria Acknowledgements

Features of the zeotropic gas mixtures studied The hydrocarbon mixtures are formed by 3 and 4 components. The synthetic refrigerant mixtures have 4 and 5 components. Generally, the phase change is experienced from 150 K to room temperature. We are focus in the boiling process. x = 0.75 P = 0.2 MPa x = 0.25 P = 1.2 MPa Tglide over 80 K x = 0.50 45% methane, 35% ethane, and 20% propane (molar base)

Multi-Refrigerant Joule-Thomson 5 after-cooler P = 200bar 1 T P = 20bar T recuperator HX room temperature 1 5 room temperature 1 P = 1bar 5 2 throttle valve 2 4 3 evaporator JT: low thermal efficiency low cost high reliability Scalable to small loads cold temperature 2 cold temperature 4 3 4 3 h h MRJT applications: cryosurgical probes, cooling infrared sensors, cryopreservation, liquefaction, biomedical samples, and current leads Understand the Thermodynamics of mixture, phase diagrams Heat Exchanger - Crucial component and understand the thermal behavior of gas mixtures. MRJT: higher thermal efficiency low cost AC compressor

Little correlation (2008) Based on annular flow Specific heat of the mixture Apparent specific heat of the mixture htcl and htcv single phase heat transfer coefficients are calculating using Dittus-Boelter Chisholm void fraction model is recommended to determine the hydraulic diameter for the liquid and vapor fraction Validated using Nellis et al. (2004) data. It is not clear shown how the correlation is obtained and how it should be applied.

Similar correlations Silver (1947) and Bell and Ghaly (1972) Granryd (1991)

Little derivation Mixing pot temperature Liquid vapor temperature difference

Little derivation (continuation)

Dittus-Boelter for the liquid film Little derivation (continuation) (Annulus) Dittus-Boelter for the liquid film

Little correlation final form Dittus-Boelter for the liquid film Dittus-Boelter for the vapor core Chisholm void fraction model

Validation using Nellis et al (2004) data (6) Nitrogen, methane, ethane, propane and isobutane mixtures. horizontal tube (ID= 0.835 mm). Mass fluxes = 200 - 900 kg/m2-s Pressures = 400 - 1400 kPa constant heat flux of 80 kW/m2 . AAD = 19%

Validation using Barraza et al (2015) data 2, 3, 4 and 5 components mixtures. Nitrogen-hydrocarbons mixtures Argon-Fluorochemical refrigerants mixtures. Temperatures between 100 K and room temperature. horizontal tubes (0.5 to 3.0 mm) heat fluxes = 20 - 80 kW/m2 mass flux = 140 to 250 kg/m2-s pressure of 270 and 790 kPa surface roughness effects

Validation using Barraza et al (2015) data

Data prediction

Applicability criteria Assuming Cicchitti et al. (1959) homogeneous model a dimensionless factor is defined:

Acknowledgements This work was sponsored by ASHRAE, Research Project 1602-TRP.

Solar Energy Lab Description and validation of the Little correlation for boiling zeotropic mixtures in horizontal tubes from cryogenic to room temperature Rodrigo Barrazaa,b, Gregory Nellisa, Sanford Kleina, Douglas Reindla aDepartment of Mechanical Engineering, University of Wisconsin, USA bDepartment of Mechanical Engineering, Universidad Tecnica Federico Santa Maria, Chile